'88 Merc 115hp Inline 6 Exhaust Problem

[bmbecker]

I was running my Boat today trying to get some late season fishing done and my motor suddenly made a couple banging noises, rattling noises, and soon after died. Exhaust is coming out from down below the powerhead next to the shaft instead of from the prop. Seems to me that I lost the connection to my exhaust tube but im not sure of how all the exhaust and water connections and stuff work. Water pumps through the power head and out the 'pee' hole normally and it seems as though I have at least a majority of the power that I should have as well once it is started. It will not run very well at an idle but I am assuming that it is because all the exhaust fumes and normal 2cycle smoke it pouring out right under the carbs....as soon as speed is built up and the motor catches clean air...it works MUCH better, but still makes a sort of banging noise. Does anyone have any good ideas for me to look into or any webpages to look at the show like a cutaway design of the exhaust system? Im all ears.....I have all winter now to get that thing running good now. Any help or ideas for me to try are appreciated. I thank anyone reading for your time....bmbecker!!!

 

[emckelvy]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

I'm wondering if maybe you blew a rod and there's now a hole in the crankcase. Take a strong light and check all around the block. You can also remove the lower, small wraparound cowling for further inspection of the base of the block & the exhaust adapter plate. It's held on with just (2) screw per side, they go straight up thru into the base pan.

Another thing you could do is remove all the spark plugs and check to make sure all pistons are still going up and down when you rotate the flywheel. Only rotate the flywheel in the clockwise direction (as viewed from the top of the motor), if you spin it the other way it could damage the impeller.

If you have a compression gage that'd be a good thing to check, a 'dead hole' is sure indication of major problems.

HTH & let us know what you find........ed

 

[jake505]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

not sure what the problem is there but just to add I dont think it could be a rod thrown through the case because doesn't a 2 stroke need the vacuum caused by the moving pistons to draw the fuel into the engine. and if there were a hole in the case there would be insuffiecient vacuum to even run. doesn't mean it couldn't have trown a rod just not through the case. i would check the compression on all cylinders and see how that looks that would be the best bet

 

[bmbecker]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

I will def try to take that cowling off and check out the base of the block. I know that the exhaust is coming straight up from down below and only from the front(transom side) of the motor....directly under the carbs actually. The spark plug side or the back of the motor doesnt seem to have much exhaust pouring out. But with the amount of exhaust coming out...it doest seem to me that it could be a hole in the block or case....it is the exhaust for all 6 cyl cause there was nothing coming out from the propeller under water. It was all coming out up top. Also, when it is running, it sounds like a 2cycl with NO muffler. It is very strange to me. As much work as I have done tinkering with this motor. I just dont see how it could be an internal issue...but I will def check it all out and make for damn sure that the pistons and compression are OK. Thanks for your help and anyone else with ideas please feel free to drop a line here. Im all ears...

Thanks!!!!

BMB

 

[Faztbullet]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

If you have exhaust under cowling the bottom bearing may took a dump and popped a hole in crankcase under # 3 carb. I have only seen 1 inline exhaust tube/tuner fall off but it could be your problem , have seen several V-6 tuners fall off. If this happened exhaust would exit from the front motor mount area and into bottom of cowling.

 

[daveswaves]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

not sure what the problem is there but just to add I dont think it could be a rod thrown through the case because doesn't a 2 stroke need the vacuum caused by the moving pistons to draw the fuel into the engine. and if there were a hole in the case there would be insuffiecient vacuum to even run. doesn't mean it couldn't have trown a rod just not through the case. i would check the compression on all cylinders and see how that looks that would be the best bet[/quote)]

Partially true, the hole would only affect 2 cyl, the other 4 would keep things running (you would be surprised). It might only affect one cyl, depends on where the damage is.

 

[bmbecker]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

Well, I checked the block and I have a huge hole under the bottom #3 carb. I found another block for the motor. It is a used one. Not to bad of a price either. Does anyone have any idea how much of a pain in the *** this will be to change out. I have a pretty good knowledge of mechanics, and have a friend that is huge help as well. Plus a shop full of tools and such. Only prob is neither of us really have much outboard knowledge. Any suggestions or other ideas for me, Im all ears. Im pretty open at this point. Thanks!!!

 

[Faztbullet]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

What year is the replacement block and does it have the power ports cut in cylinders? You need to go to Ebay and buy you a factory service manual or CD. Stay away from the Seloc manuals... Just my $.02

 

[daveswaves]

Re: '88 Merc 115hp Inline 6 Exhaust Problem

Well, I checked the block and I have a huge hole under the bottom #3 carb. I found another block for the motor. It is a used one. Not to bad of a price either. Does anyone have any idea how much of a pain in the *** this will be to change out. I have a pretty good knowledge of mechanics, and have a friend that is huge help as well. Plus a shop full of tools and such. Only prob is neither of us really have much outboard knowledge. Any suggestions or other ideas for me, Im all ears. Im pretty open at this point. Thanks!!!

The block is easy to change out, the main thing to beconcerned with is the condition of the replacement block and the vintage. Early 115 blocks were notpower ported and compared to your 88 they would only be 90 hp. Going rate for a completely rebuilt block is in the $1200 mark, sometimes less.